Cooper cleared Boston 23 July 1944 for Pearl Harbor arriving 4 September. After operational training, she sailed 23 October for Ulithi, arriving 5 November, and put to sea at once to screen carriers in air attacks on Luzon, Ormoc Bay and Manila Bay until 19 November. After repairs at Ulithi, she entered San Pedro Bay, P.I., 29 November and joined in patrols in Leyte Gulf until 2 December, when she sailed with Allen M. Sumner (DD 692) and Moale (DD 693) to destroy shipping in Japanese-held Ormoc Bay. Here the ships gallantly engaged two small enemy destroyers and numerous small craft.

At about 0013 on 3 December, Cooper was torpedoed, suffered an explosion on her starboard side, broke in two and sank within a minute. The presence of enemy forces prevented rescue of survivors until about 1400, when “Black Cat” aircraft were able by sheer daring to save 168 of Cooper’s crew. Lost were 191.